What Causes Severe Pain In Lower Abdomen?

I have horrible, wrenching pain in my lower abdomen. I get this about every 2 to 3 months where it debilitates me for at least 2 to 3 hours. I sweat it hurts so bad. The pain comes and goes and finally stops, I ve tried to pinpoint it. It mostly happens around my period, but not always. It s mostly in the center to left side. It s been happening the last year or so. I just remember it being excruciating last Chistmas day and this most recent one. My husband thinks it s gas, so I take gas X, which doesn t help immediately. My periods have gotten a lot worse too, since I haven t taken the pill for the last 4 to 5 years. Last time I almost passed out when blood seemed to be streaming from me. I didn t know how else to put it. I get queasy easily. Previous to that, I have taken the pill most of my life. Obviously, I am a female. I m 44 and never had children, I have never had any surgery. I work out 4 to 5 times a week with bikram yoga or Kick boxing. I m 5 4 and weigh between 132 and 137 depending on how much I ate over the holidays! Thanks so much.